Calculating optimum CFM for rotaries

dr.occa · 03-01-2013, 09:36 PM

I've been going over some math in determining various carb options for the rotary motors. I'm very familiar with the tried and true IDAs (running one on my 12A), DCOEs & 44PHH (running a pair on my 4AG) and the 4 barrels: what I'm scratching my head about is do I use the cc displacement at the taxed 720° rotation or the actual full 1080° rotation in calculating optimum CFM?

Here are the answers for my 12A using both displacement numbers (in cubic inches):

((8000[rpm] x 140cc[rounded up from 139.866421]) / 3456) X .85 = 275.46CFM

((8000 x 210cc[rounded up from 209.7996322158]) / 3456) X .85 = 413.2CFM

Which should it be?

03-01-2013, 09:36 PM	#1
dr.occa Rotary Fan in Training Join Date: Mar 2011 Posts: 73 Rep Power: 15	Calculating optimum CFM for rotaries I've been going over some math in determining various carb options for the rotary motors. I'm very familiar with the tried and true IDAs (running one on my 12A), DCOEs & 44PHH (running a pair on my 4AG) and the 4 barrels: what I'm scratching my head about is do I use the cc displacement at the taxed 720° rotation or the actual full 1080° rotation in calculating optimum CFM? Here are the answers for my 12A using both displacement numbers (in cubic inches): ((8000[rpm] x 140cc[rounded up from 139.866421]) / 3456) X .85 = 275.46CFM ((8000 x 210cc[rounded up from 209.7996322158]) / 3456) X .85 = 413.2CFM Which should it be? Last edited by dr.occa; 03-01-2013 at 09:40 PM.